Ligaments are strong fibrous connective soft tissue which connect the articular ends of bones to bind them together and to facilitate or limit motion. Injuries to ligaments are common, and patients who are physically active are generally more susceptible to such ligament injuries. The anterior cruciate ligament (ACL) of the knee joint is a ligament frequently injured by such patients. Such injuries cause instability in the knee joint which, when left untreated, may lead to degenerative arthritis. Because of this condition, ACL reconstruction may be required. Generally during ACL reconstruction, a substitute soft tissue ligament or graft is attached to the femur and/or tibia to facilitate regrowth and permanent attachment.
One method of performing this reconstruction involves the use of a section of bone-patellar tendon-bone as a graft. With this method, a ligament tunnel is bored into both the femur and the tibia and the bone-patellar tendon-bone graft is centered between the tunnel. The bone portions of the graft are then each secured within the respective tunnel by tightening an interference screw in each tunnel between the bone graft and the side of the tunnel.
However, use of such a technique presents several disadvantages. For example, the graft may be inadvertently cut or frayed by the sharp edges of the interference screw during insertion of the screw and subsequent to fixation. Moreover, if the interference screw or the bone graft is slightly oversized versus the size of the tunnel, the interference screw may cause too much force to be exerted on the bone graft portion as the interference screw is tightened. This may subsequently cause the bone graft portion to be damaged and not usable. In addition, it is often difficult to accurately, gauge the length of the bone-patellar tendon-bone graft in relation to the ligament tunnels such that the bone graft portions may not seat appropriately within the tunnels or be properly tensioned.
Another method for performing this reconstruction involves the use of only a soft tissue ligament graft. Such a graft is generally taken from the hamstring ligament, specifically, the semitendinosus and gracilis ligaments or tendons. Such grafts are generally fed through the ligament tunnel and secured outside the tunnel. The graft is generally secured by a non-endoscopic means of stapling or screwing the graft onto the outside surface of the tibia and/or femur.
However, this method of securing the soft tissue graft also exhibits disadvantages. For example, since the various staple or screw and washer assemblies in existence are positioned on the outside of the bone surface or extend beyond the bone surface, such components are more easily noticed by the patient and in some instances may cause patient discomfort. In addition, because of the discomfort, it may be required to perform subsequent surgery to remove the staple or screw and washer assembly once the graft has permanently attached to the bone, thereby subjecting the patient to a second surgery, as well as increasing overall surgical costs. The staple or screw and washer assembly are also not substantially resistant to slippage and do not provide stiff securement. In other words, the graft may permanently slip under the securement of the staple or screw and washer assembly thereby providing a non-optimum tension on the graft. Securement at the anchoring point may be resilient such that if the graft utilizes sutures in combination with the staple or screw washer assembly, the anchoring point may stretch under stress and resiliently return, thereby also providing non-optimum tensioning or stiffness for the graft.
Another method for securing the soft tissue ligament graft within a femoral tunnel is set forth in U.S. Pat. No. 5,431,651. This reference uses a cleated washer which engages the soft tissue graft within the femoral tunnel by use of a transverse cannulated set screw. The cleated washer is drawn into the femoral tunnel by use of a suture coupled to the washer and pulled through the cannulated set screw. Once in position adjacent to the set screw, the set screw engages the cleated washer against the soft tissue ligament and the wall of the tunnel.
However, this method of securing a soft tissue graft within a femoral tunnel also exhibits many disadvantages. For example, such a procedure will generally require more surgical time since it includes the added steps of passing a suture through a cannulated set screw and down the femoral tunnel, as well as attaching it to the cleated washer itself. This also makes it extremely difficult to properly align the cleated washer since the cleated washer must be pulled through and aligned using a flexible non-rigid suture. Additionally, it may be difficult to maintain the location of the cleated washer as the set screw is engaged against the washer since the suture does not rigidly hold or maintain the position of the cleated washer. Finally, by drawing the cleated washer up through the femoral tunnel, a larger femoral tunnel may be required and the spikes on the cleated washer may cut or fray the soft tissue graft as it is passed through the femoral tunnel.
What is needed then is an apparatus and method for tibial fixation of a soft tissue graft which does not suffer from the above-identified disadvantages. This in turn, will reduce the possibility for damaging the soft tissue graft; reduce the possibility for requiring a new graft from being harvested; provide for endoscopic securement of a soft tissue graft without damaging the graft; reduce or eliminate potential patient discomfort; provide endoscopic fixation which is flush to the bone surface; reduce or eliminate the need for a subsequent surgery to remove fixation components after the graft has been permanently attached to the bone; provide increased fixation strength; provide less pretensioning of the graft to restore knee stability, thereby not over-constraining the knee after setting the tension on the graft; reduce or eliminate the potential for slippage of the soft tissue graft; increase stiffness and mechanical behavior of the soft tissue graft; reduce the number of steps to secure the soft tissue graft; and reduce the number of separate instrumentation required to secure the soft tissue grafts. It is, therefore, an object of the present invention to provide such an apparatus and method for tibial fixation of a soft tissue graft.